1. Field of the Invention
The present invention is broadly concerned with an improved process for the preparation of granular cold water-soluble starches (GCWS) which involves heating of a starch slurry comprising water, polyhydric alcohol and starch granules for converting the native partially crystalline starch to cold water-soluble granules with V or amorphous-type x-ray patterns. More particularly, it is concerned with such process which may be carried out at atmospheric pressure and with moderate amounts of polyhydric alcohol solvent to yield finished cold water-soluble starches. Pastes made from GCWS starches in cold to warm water systems are comparable to those of cook-up starches in smoothness of texture, sheen, cold-storage stability, and gelling properties.
2. Description of the Prior Art
Pre-gelatinized or instant starches are used in the preparation of many commercial food products. These instant starches are designed to swell and paste at low to warm temperatures. In the conventional processes for making instant starches, a starch slurry is simultaneously cooked and dried on a drum dryer to give a thin sheet, which is subsequently ground to a fine powder. Such drum-cooked instant starches often give inferior performance in foods as compared with cook-up starches. This is believed to result from the fact that on the hot drum, the cooked granules fuse together and are strongly cemented to form a starch sheet. Fine grinding of the sheet gives irregularly shaped particles that contain retrograded starch, leading to a grainy appearance upon rehydration. Furthermore, drum-cooked instant starches have reduced consistency upon rehydration to a paste and form gels of reduced strength.
In recent years methods have been developed to give pre-gelatinized starches with granular integrity. Some granular cold water-soluble starches hydrate without lumping in cold to warm solutions of sugar or other strongly hydrating food components, and their pastes are on a par with typical cook-up starches. Others hydrate in cold water without lumping, but have reduced capacity to generate thickening power.
U.S. Pat. No. 4,280,851 describes a process using a spray-drying chamber and a specialized nozzle. The nozzle atomizes a mixture of water and starch in a small chamber inside the nozzle, while steam is injected into the small chamber through a second opening. The moistened starch-steam mixture is retained in the chamber long enough to effect gelatinization of the starch granules, after which time the rapidly moving granules exit the chamber through a vent aperture and fall into a fluid-bed drying chamber.
U.S. Pat. No. 4,465,702 describes a method for the production of granular cold water-soluble corn starch wherein a slurry comprising of corn starch, water and a monohydric alcohol are heated under elevated pressures of from about 400-600 psig. This process is deemed deficient in that it requires a high pressure vessel. Moreover, normal corn starch and octenylsuccinylated corn starch were the only starches converted to the new physical form.
E. M. Montgomery and F. R. Senti in J. Polymer Sci. 28(1958)1 described a treatment of corn, wheat and potato starches with 70-85% aqueous organic solvents at 89.degree. C. The solvents included glycerol, cellosolve, n-butanol, dioxane and pentasol. After removal of the aqueous organic solvent mixture by solvent exchange and drying, pre-treated starches gave improved leaching of amylose when heated in water. The authors preferred pretreatment with hot 85% aqueous organic solvents, gave no loss of birefringence of the starch granules. The authors did report loss of birefringence in hot 70% aqueous glycerol.